Many electronic devices are tested for electrical and optical properties during manufacturing by automated test systems. Typical automatic test systems use precision electrical or optical test equipment to find values associated with electrical and optical properties of a device and either accept, reject or sort it into an output category depending upon the measured values. For miniature devices, automatic test systems are often designed to handle bulk loads, where the manufacturing process creates a volume of devices which have substantially identical mechanical characteristics such as size and shape but differ in electrical or optical characteristics. It is common practice to build a volume of devices with electrical and optical properties which generally fall within a range and rely on testing to sort the devices into commercially useful groups with similar characteristics.
These devices are often supplied to the test equipment as containers filled with devices. Typically the test equipment must extract a single device from the bulk load of devices, orient the device and fixture it so the test equipment can perform the desired tests. Testing often requires probing the device, wherein electrical leads are brought into contact with device to permit signals and power to be applied to the device and to monitor responses to the inputs. Other tests involve measuring light output from optical devices such as LEDs in response to specific inputs. The task of the automatic test system is to determine the electrical or optical characteristics of devices and sort the devices into groups depending upon those characteristics.
Testing and sorting LEDs is particularly challenging because the wide variance in manufacturing tolerances and the sensitivity of the human eye to small variations in light output combine to require that LEDs be tested and sorted into a large number of output groups. While passive electronic devices might typically require five or ten output categories, LEDs might typically require in excess of 32 output categories up to as many as 512 categories. Other challenges associated with testing and sorting LEDs includes the fact that LEDs need to have their light output tested. Since LEDs can have contacts on one side of the package and light emitting surfaces on the other, the test equipment must probe from one side and collect light output from the other. Another challenge is that light output test equipment is often physically large and needs to be in proximity to the LED under test, which constrains the physical layout of the test equipment. In addition, if parallel testing is to be performed, where multiple test stations are arranged to test multiple devices simultaneously, room for multiple bulky optical test stations needs to be arranged.
Rotary feeders have been recognized as an efficient way to load and orient small parts. U.S. Pat. No. 6,220,481 SEPARATING FEEDER FOR CHIP COMPONENTS, inventor Masayuki Miyamoto, Apr. 24, 2001 uses a rotating grooved disk to orient and load parts into cavities which maintain the part orientation. U.S. Pat. No. 7,119,299 WORK INSPECTION SYSTEM, inventor Tomoyuki Kojima, Hiroaki Abe, Shigeru Matsukawa, Takahiko Iwazaki and Takayuki Yamauchi, Oct. 11, 2006 describes a system with a vertical rotary disk to orient and hold parts delivered by gravity to a face of the disk. U.S. Pat. No. 5,842,579 ELECTRICAL CIRCUIT COMPONENT HANDLER, inventors Douglas J. Garcia, Steven D. Swendrowski, Mitsuaki Tani, Hsang Wang, Martin J. Twite, III, Malcolm Hawkes, Evart David Shealey, Martin S. Voshell, Jeffrey L. Fish and Vernon P. Cooke, Dec. 1, 1998, assigned to the assignee of this invention, discloses a rotary disk test machine with multiple tracks able to test multiple parts at once. U.S. Pat. No. 4,747,479 DEVICE FOR THE TESTING AND/OR PROCESSING OF SMALL COMPONENT PARTS, inventor Jakob Herrman, May 31, 1988 discloses a linear belt to hold parts under test. What these disclosures do not consider are the particular demands that testing LEDs places on equipment including requirements for accessible fixturing, the need for large numbers of output bins and handling large and bulky optical test equipment.
In particular it is desirable to sort electro-optic devices such as singulated LEDs into groups depending upon electrical and/or optical properties. One system designed to perform such sorting is the LED Die Brightness/Wavelength Sorter Mode ALPHA 3200/3200F manufactured by E-Globaledge Corporation, Tokyo, Japan. This system measures an LED die's brightness and wavelength output at the same time and classifies them into a maximum of 32 tracks. It performs the optical tests in 0.8 seconds, while performing no electrical tests. Assuming an overhead factor of 50% to perform indexing of the LED to and from the test station, this would yield a system throughput of about 3000 units per hour (UPH). It would be desirable to be able to test both electrical and optical properties of an LED with the same system in order to save expense and floor space in the test facility. It would also be desirable to be able to test and sort LEDs at a much higher rate of speed in order to minimize the number of systems required to test and sort a given production volume of LEDs. In addition it would be desirable to be able to sort the tested LEDs into more than 32 different categories.
What is needed, then, is an LED test and sort system that can test both electrical and optical properties of an LED, test and sort them at high speed and sort them into more than 32 different categories following testing.